Orientational ordering of C₆₀ in the antiferromagnetic (NH₃)K₃C₆₀ phase

The absence of superconductivity in the ammoniated alkali fulleride, (NH₃)K₃C₆₀, and the transition to an antiferromagnetic (AF) Mott insulating ground state have been associated with the combined effects of crystal symmetry lowering and increased interfullerene separation. We find that the low-temperature orientational ordering motif of the C₆₀ units in the perdeuterated analog, (ND₃)K₃C₆₀, correlates well with the three-dimensional AF structure proposed by NMR, which arises through alternate stacking of two-dimensional sheets of C₆₀, which order ferrorotationally (antiferromagnetically) along the 〈110〉 and antiferrorotationally (ferromagnetically) along the 〈11̄0〉 directions.